added first test case for changeOrderInSavedPlaylist() & and added productive code

src/main/java/device/radioPlayer/RadioPlayer.java

@@ -210,4 +210,11 @@ public class RadioPlayer implements Device {
         }
         return "You are already in saved Playlist!";
     }
+
+    public String changeOrderInSavedPlaylist(int nr) {
+        String station = playedStation;
+        savedPlaylist.remove(playedStation);
+        savedPlaylist.add(nr-1,station);
+        return"Station " + playedStation + " is now on place 0" + nr + "in saved playlist";
+    }
 }

src/test/java/device/radioPlayer/RadioPlayerTest.java

@@ -265,4 +265,21 @@ class RadioPlayerTest {
 
         );
     }
+
+    @ParameterizedTest
+    @MethodSource("changeOrderInSavedPlaylistOptions")
+    void testChangeOrderInSavedPlaylist(String testName, RadioPlayer testRp, int nr, String expectedResult) {
+        String savedStation = testRp.savedPlaylist.get(nr);
+        assertThat(savedStation).describedAs(testName).isEqualTo(expectedResult);
+    }
+
+    static Stream<Arguments> changeOrderInSavedPlaylistOptions() {
+        RadioPlayer rp = new RadioPlayer();
+        rp.next();
+        rp.changeOrderInSavedPlaylist(1);
+
+        return Stream.of(
+                Arguments.of("Test for change order in saved playlist with nr isn`t than playlist size", rp, 0, "Teddy")
+        );
+    }
 }